This invention relates generally to wire bonding tools for use in the semiconductor and electronic industry and more particularly to wire bonding wedges.
In U.S. Pat. No. 3,627,192, owned by the assignee of this application, there is described a wire bonding tool of the capillary or wedge type including a shank of a material having a high modulus of elasticity such as tungsten carbide with one end portion forming a welding tip. A wire guiding hole presents the wire to be bonded to the tip. The end portion of the tool is made of osmium to provide an improved bond and increased tool life. Other bonding wedges of various shapes and designs are known.
One of the difficulties experienced with the wire bonding wedges of the prior art is that the guide opening is generally cylindrical and only slightly larger than the wire to be bonded. The build-up of dirt and other debris tends to easily plug the hole and strain the wire. Furthermore, the width of the tip, in order to accommodate an opening of predetermined cross-sectional area, is large. This interferes with viewing of the bonding area by the operator.
When the bonding wedge is lifted and translated after a bond, there tends to be abrasion of the wire because of the change in angle of the wire with respect to the horizontal.
Since bonding tools are relatively small, it is difficult to thread the wire through the guide opening. In the past, the end of the opening has been enlarged in the form of a cone to thereby present a larger insertion area for the thin wire lead material.
In summary, prior art tool tips have been wider than desired, guide holes are subject to plugging, tend to abrade the wire, and fail to control the wire in feeding up the bonding pads.